Over the past two years the World Health Organization and the U.S. Dietary Guidelines have begun urging us to consume no more than 10 percent of our daily calories from added sugar. Drinking more than one sugar-sweetened soda a day can put you over that limit.

But a new industry-funded study published in a prominent medical journal questions the evidence used to generate the specific recommendations to limit sugar in our diets.

"Overall, I would say the guidelines are not trustworthy," says study author Bradley Johnston, a clinical epidemiologist at the Hospital for Sick Children in Toronto who also teaches biostatistics.

Johnston reviewed the studies and methodology used to generate the guidelines. He concludes that while it's wise for people to limit sugar consumption, there's still a question about how much to limit.

"Sugar should certainly be limited in the diets of children and adults, no question," he says. But he argues there's not convincing evidence to support cutting consumption to 10 percent, or 5 percent — or any specific threshold.

"There's a lot of uncertainty about the thresholds that appear in guidelines," Johnston says. "What's happening is that guideline panelists are making strong recommendations based on low-quality evidence." (The paper reviewed nine sugar-intake guidelines from around the globe, included the WHO guideline and the Dietary Guidelines for Americans, which were updated this year.)

The paper, which appears Monday in the Annals of Internal Medicine, has raised the ire of public health experts. "We should reject these findings," says Dean Schillinger, a physician at the University of California, San Francisco and advocate for diabetes-prevention efforts.

Schillinger has penned an editorial, published alongside the study, that's titled, "Guidelines To Limit Added Sugar Intake: Junk Science or Junk Food?" He writes that the new paper amounts to "the politicization of science."

Schillinger says that when you look at the body of evidence, the science is clear. "Nearly all experimental studies that examined whether eating added sugars contributes to obesity and [Type 2] diabetes-related outcomes show a cause-and-effect relationship," Schillinger told us.

Marion Nestle, a nutrition professor at New York University who has written extensively about the soda industry, says this new paper is an attempt by big food and beverage companies to use their power to undermine the scientific consensus on limiting added sugars in our diets.

"This is a classic example of industry-funded research aimed at one purpose and one purpose only: to cast doubt on the science linking diets high in sugars to poor health," Nestle tells us. "This paper is shameful."

The paper was funded by the International Life Science Institute. The group is financially supported by food and beverage companies including McDonald's Corp., Mars Inc., The Coca-Cola Co. and PepsiCo Inc.

"This is not an industry attempt to undermine the science," Eric Hentges, the executive director of ILSI, North America, told us. He says the aim of the paper is to examine the inconsistencies in sugar guidelines around the globe and to examine the science behind the specific recommendations. "The purpose of the paper was to investigate specifically the quality of methods and the quality of evidence," Hentges told us.

I asked study author Johnston for a specific example of a study that exemplifies the uncertainties in the scientific evidence on sugar intake. He pointed me to one published in the New England Journal of Medicine in 2012.

That study included 224 overweight and obese adolescents who regularly consumed sugar-sweetened beverages. The participants were divided into two groups. The experimental group received noncaloric beverages at home and were told to cut out sugar-sweetened beverages. The control group kept up their normal pattern of consumption.

At the end of the first year of the study, the participants who received the noncaloric beverages at home had smaller increases in body mass index compared with the control group. But by the end of the second year, "there was no difference between groups," Johnston says.

Johnston says the point he wants to make is that sugar intake is not the only factor related to obesity and Type 2 diabetes. "It's one factor among many," Johnston says. He says scientists should not put "ourselves into an ideological framework where we think that sugar is the scapegoat for the rise in obesity and diabetes."

The concern among public health experts is that this position — and this new paper published in Annals — could be used as a justification for questioning the dietary guidelines for sugar.

"The big picture here is we're talking about a fundamentally threatening [Type 2] diabetes epidemic," Schillinger told us. "Fourteen percent of Americans — that's 1 in 7 adults — have diabetes." And he says questioning the science behind specific recommendations should not distract from the effort to nudge people to consume less sugar.

Schillinger says this study and other industry efforts around sugar remind him of tactics used by Big Tobacco. "This is very reminiscent of what tobacco did around secondhand smoke," he says.

When studies showed harm related to secondhand smoke, "the [industry] called that science junk science. It was really an attempt to undermine the scientific process and create additional doubt in the general public," Schillinger says.

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ARI SHAPIRO, HOST:

One food trend that will continue into 2017 is the continued push sodas and snacks with less sugar. The World Health Organization and other expert groups say high-sugar diets have helped fuel the rise in Type 2 diabetes and obesity. It's not clear how much people need to cut back on sugar. While there are specific recommendations a new battle erupted today in the pages of a prominent medical journal over the evidence behind them. NPR's Allison Aubrey reports.

ALLISON AUBREY, BYLINE: Over the last two years, new guidelines from the World Health Organization and then the U.S. government began urging Americans to consume no more than 10 percent of our daily calories from sugar. That amounts to about one sugar-sweetened soda a day. But Bradley Johnston, a researcher at the Hospital for Sick Children in Toronto who reviewed all the studies used to generate the guidelines, has concluded there's still a question about what the recommended limit should be.

BRADLEY JOHNSTON: Overall I would say that the guidelines are not trustworthy.

AUBREY: Before we go any further, I should point out that Johnston's study was funded by an industry group called the International Life Sciences Institute. It receives funding from companies including Coca-Cola, Pepsi, the candy maker Mars and McDonald's. But Johnston says he carried out his analysis independently. He says while it is wise to limit sugar, he argues there's not convincing evidence to support cutting back sugar intake to 10 percent or any other specific threshold.

JOHNSTON: There's a lot of uncertainty about the thresholds that appear in guidelines. And what's happening here is guideline panelists are making strong recommendations based on low to very low quality evidence.

AUBREY: This conclusion has drawn the ire of public health experts. Marion Nestle of New York University says this paper is an example of the industry using its weight to undermine the scientific consensus on sugar.

MARION NESTLE: It's a classic example. It's industry-funded authors saying that the dietary guidelines recommendations about sugar aren't based on science. I'm laughing because what kind of evidence do you need? Sugar is calories and no nutrients and everybody would be healthier eating less of it.

AUBREY: Eric Hentges is the executive director of the industry-funded group that sponsored the study. He refutes this accusation.

ERIC HENTGES: This is not an industry attempt to undermine the science.

HENTGES: The purpose of the paper was to investigate specifically the quality of methods and the quality of evidence.

AUBREY: This argument does not convince Dean Schillinger. He's a physician at UC San Francisco and an advocate for diabetes prevention efforts. He's written an editorial that is published alongside the new study in the Annals of Internal Medicine.

DEAN SCHILLINGER: This is very reminiscent of what tobacco did around secondhand smoke when there was a question as to whether secondhand smoke, you know, killed people. And they called that science junk science. And it was really an attempt to undermine the scientific process and create additional doubt in the general public so that regulatory outcomes would not be in their disfavor.

AUBREY: Schillinger says when it comes to the effect of a high-sugar diet, there's no question that people should limit their sugar consumption.

AUBREY: And he says questioning the science behind the specific recommendations should not distract from the effort to nudge people to consume less sugar. Allison Aubrey, NPR News. Transcript provided by NPR, Copyright NPR.